slightly swollen new cells - acceptable?

[Nevadageo]

A few days ago I received my order of 4 LiFePO4 batteries, and noticed they were slightly swollen.


Being a newbie I didn't think much of it and started top balancing them. Today I realized the swelling was not a good thing and stopped the top balancing at 3.35 Volts. They hadn't swelled beyond the condition received. When pushed tightly together there is a gap between the top edges of 4 to 5 mm.



Is this amount of swelling normal, or acceptable, or should I send them back?

 

[Immortal Lu]

I have the same set of cells with 2 slightly swollen. I still plan to top balance and measure capacity. If it goes well, I think I'll build the battery anyway. My construction plan is to have rigid spacing along the cell edges, and hose clamps to hold it together so the centers of the cases are not compressed. Not sure if its the best plan, but I need a battery before I could get replacement cells.

 

[Nevadageo]

Thanks, Immortal Lu. Your answer lead me to study more about this amount of swelling with new batteries, and evidently it is not uncommon. Part of LiFePO4 batteries "breathing" - expanding and contracting slightly as they charge and discharge. It's not optimal, but since the batteries have not been overcharged it is not necessarily a danger sign. I will top balance, measure capacity, etc. and if all is well build the battery with the cells compressed between plates, so the cells are held flat, but at no more than 12 psi. A bit different from your plan but I read elsewhere that it's not necessary to leave room for expansion, and partial compression, not too much, can improve the life of the batteries.

 

[Coop]

Hello I just received my 16pcs of 120Ah cells from BLS Battery. (Advertised as New 2021 A Grade cells)
These are the pictures taken right after unboxing the first 4pcs and attaching the studs.
Some degree of swelling, they will not fit snugly against each other. I top balanced them to 3.65V with a CV/CC charger, (all 4 were, 3.290V).
Attached the BMS (OverkillSolar 120A 4S) charged them up and did a capacity test (at 0.35C) , and surprise they pulled a full 120Ah actually 125Ah, when my inverter disengaged due to low voltage at 10.8V no cell went below 2.550V and BMS did not disengage due to low voltage.
Conclusion. the first 4 cells are ok, even they are a bit swollen.
I will try to flatten them by laying flat and applying some weight 2-4Kg for a couple of hours just to see if they even out.
Now working on the rest set of 12 cells.

 

[MisterSandals]

I will try to flatten them by laying flat and applying some weight 2-4Kg for a couple of hours just to see if they even out.

So they pulled a full capacity test and appear to be functioning well but you are compelled to "fix" them?

 

[Coop]

So they pulled a full capacity test and appear to be functioning well but you are compelled to "fix" them?

Basically just out of curiosity, to see if they actually flattens out.
I have a compression case in the making with some progress.

I was a long time under the impression that even the slightest swollen cells were bad, and not acceptable.
(even Will talks about this in his vids)

Just after reading tons of threads here on the forum, about alu case cells "breathing" and acceptance of a slight swelling, and ppl applying slight weights to try to flatten them out, was I reassured that if the cells pull full capacity and no runaways during discharge/charge the cells
are ok, even if a bit swollen at arrival.